63 



The smallest specimen which I have found (fig. .3) had already the characteristic he- 

 mispherical form. The upper convex surface had only one fistular osculum in the centre. 

 The circular rim of spicula was already completely developed; and its width was equal to 

 V 3 of the transverse diameter of the sponge. 



When the sponge is dried, the upper convex side sinks considerably ; so that it be- 

 comes nearly Hat, which justifies the supposition that its interior is of a very loose texture. 

 This is also easily ascertained by cleaving a fresh or spirit specimen along the middle. It 

 then appears (see fig. 4) to enclose a rather large cavity filled with soft parenchym, wherein the 

 interior support or skeleton formed of spicula is only very slightly developed. But on the other 

 hand the dermal stratum is particularly thick, and of very firm consistency, owing in a great 

 measure to the numerous siliceous spicula, with which it is filled. This cortical stratum is 

 sharply distinguished from the interior parenchym, and has its greatest thickness in the middle 

 of the lower side, where it occupies about Va f the height of the whole sponge, but be- 

 comes gradually thinner towards the periphery; on the upper convex side, the cortical stratum 

 is on the contrary everywhere of uniform thickness, and about half as thick as in the middle 

 of the lower side. The inner cavity, filled with sarcode, has therefore a crescent-like section, 

 as the thickened lower cortical stratum rises in the centre like a watch glass. In this interior 

 sarcode-cavity may be distinguished many irregular cavities anastomosing with each other, 

 and bounded by thin lamellae of parenchym, which are partly supported by spicula arranged 

 in fascicles. These cavities shew on the whole a radial arrangement, and have their out-let 

 above in a greater or less number of cylindrical tubes which pierce the cortical stratum, and 

 open each at the end of one of the exterior fistular processes. The whole upper cortical 

 stratum seems moreover to be perforated with particularly fine pores, through which the 

 water is led into the interior of the sponge, to be afterwards emptied out through the 

 fistular oscula. 



The spicula are of 4 different kinds, which yet have all the same general form, namely 

 the simple needle-shape. In the interior parenchym of the sponge there are found spi- 

 cula almost exclusively of one sort (fig. 11) long, straight and somewhat fusiform or tapering 

 at both ends, but so that one end always forms a bulbous enlargement (fig. 13) while the 

 other terminates in a fine elongated point (fig. 12). These spicula, which thus according to 

 Bowerbank's terminology must be called ,,fusiformi-acuate" are of very different length (from 

 0.60 to 5.40 Mm.) and have an evident axial canal. They are connected in long ramified 

 fascicles which radiate (see fig. 4) from a point lying in the centre of the periphery of the 

 sponge, but nearer to the lower than to the upper surface, or near the most prominent part 

 of the lower cortical stratum in the interior of the sponge. These fascicles of spicula sup- 

 port the thin lamellae of the parenchym which divide the interior cavity, and thence penetrate 

 into the upper cortical stratum to the greater part of its thickness, yet without reaching to 

 the extreme dermal layer (see fig. 5). In the lower cortical stratum, these fascicles are still 

 much closer, and radiate on all sides almost horizontally, penetrating not the thickness, but 



